Journal cover Journal topic
Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
Wind Energ. Sci., 2, 415-437, 2017
https://doi.org/10.5194/wes-2-415-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research articles
04 Aug 2017
Aeroelastic stability of idling wind turbines
Kai Wang1, Vasilis A. Riziotis2, and Spyros G. Voutsinas2 1China-EU Institute for Clean and Renewable Energy, Huazhong University of Science and Technology, 1037 Luoyu Rd, Wuhan, China
2School of Mechanical Engineering, National Technical University of Athens, 15780 Athens, Greece
Abstract. Wind turbine rotors in idling operation mode can experience high angles of attack within the post-stall region that are capable of triggering stall-induced vibrations. The aim of the present paper is to extend the existing knowledge on the dynamics and aerodynamics of an idling wind turbine and characterize its stability. Rotor stability in slow idling operation is assessed on the basis of nonlinear time domain and linear eigenvalue analyses. The aim is to establish when linear analysis is reliable and identify cases for which nonlinear effects are significant. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First, the flow conditions that are likely to favor stall-induced instabilities are identified through nonlinear time domain aeroelastic simulations. Next, for the above specified conditions, eigenvalue stability analysis is performed to identify the low damped modes of the turbine. The eigenvalue stability results are evaluated through computations of the work done by the aerodynamic forces under imposed harmonic motion following the shape and frequency of the various modes. Nonlinear work characteristics predicted by the ONERA and Beddoes–Leishman (BL) dynamic stall models are compared. Both the eigenvalue and work analyses indicate that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the nonlinear work analysis and the time domain simulations.

Citation: Wang, K., Riziotis, V. A., and Voutsinas, S. G.: Aeroelastic stability of idling wind turbines, Wind Energ. Sci., 2, 415-437, https://doi.org/10.5194/wes-2-415-2017, 2017.
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Short summary
In the paper, rotor stability in slow idling operation is assessed on the basis of nonlinear time domain and linear eigenvalue analyses. A consistent and computationally cost effective modeling environment has been presented for the analysis of parked or idling rotors. The analysis shows that the lowest damped modes of a 10 MW idling rotor are out-of-plane modes (symmetric and asymmetric).
In the paper, rotor stability in slow idling operation is assessed on the basis of nonlinear...
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